U.S. patent application number 16/086037 was filed with the patent office on 2020-09-17 for induction heated aromatization of higher hydrocarbons.
This patent application is currently assigned to HALDOR TOPSOE A/S. The applicant listed for this patent is HALDOR TOPSOE A/S. Invention is credited to Kim AASBERG-PETERSEN, Poul Erik HOJLUND NIELSEN, Peter Molgaard MORTENSEN.
Application Number | 20200290003 16/086037 |
Document ID | / |
Family ID | 1000004899156 |
Filed Date | 2020-09-17 |
United States Patent
Application |
20200290003 |
Kind Code |
A1 |
HOJLUND NIELSEN; Poul Erik ;
et al. |
September 17, 2020 |
INDUCTION HEATED AROMATIZATION OF HIGHER HYDROCARBONS
Abstract
A reactor system for aromatization of higher hydrocarbons within
a given temperature range T upon bringing a reactant stream
including higher hydrocarbons into contact with a catalytic
mixture. The reactor system includes a reactor unit arranged to
accommodate a catalytic mixture. The catalytic mixture includes a
catalyst material and a ferromagnetic material. The catalyst
material is arranged to catalyze the aromatization of higher
hydrocarbons. The ferromagnetic material is ferromagnetic at least
at temperatures up to an upper limit of the given temperature range
T, where the temperature range T is the range from between about
400.degree. C. and about 700.degree. C. or a subrange thereof. The
reactor system also includes an induction coil arranged to be
powered by a power source supplying alternating current, whereby
the ferromagnetic material is heated to a temperature within the
temperature range T by means of an alternating magnetic field.
Inventors: |
HOJLUND NIELSEN; Poul Erik;
(Fredensborg, DK) ; MORTENSEN; Peter Molgaard;
(Roskilde, DK) ; AASBERG-PETERSEN; Kim; (Allerod,
DK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HALDOR TOPSOE A/S |
Kgs. Lyngby |
OK |
US |
|
|
Assignee: |
HALDOR TOPSOE A/S
Kgs. Lyngby
DK
|
Family ID: |
1000004899156 |
Appl. No.: |
16/086037 |
Filed: |
March 31, 2017 |
PCT Filed: |
March 31, 2017 |
PCT NO: |
PCT/EP2017/057670 |
371 Date: |
September 18, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C07C 2/42 20130101; C07C
2523/06 20130101; B01J 8/0285 20130101; B01J 2208/00433 20130101;
C07C 2529/85 20130101; B01J 29/85 20130101; C07C 2529/06 20130101;
B01J 29/061 20130101; B01J 35/0033 20130101; B01J 23/862 20130101;
B01J 8/025 20130101; B01J 8/0278 20130101 |
International
Class: |
B01J 8/02 20060101
B01J008/02; B01J 23/86 20060101 B01J023/86; B01J 29/06 20060101
B01J029/06; B01J 29/85 20060101 B01J029/85; B01J 35/00 20060101
B01J035/00; C07C 2/42 20060101 C07C002/42 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 26, 2016 |
DK |
PA 2016 00245 |
Claims
1. A reactor system for aromatization of higher hydrocarbons within
a given temperature range T upon bringing a reactant stream
comprising higher hydrocarbons into contact with a catalytic
mixture, said reactor system comprising: a reactor unit arranged to
accommodate a catalytic mixture, said catalytic mixture comprising
a catalyst material and a ferromagnetic material, where said
catalyst material is arranged to catalyze the aromatization of
higher hydrocarbons and said ferromagnetic material is
ferromagnetic at least at temperatures up to an upper limit of the
given temperature range T, wherein the given temperature range T is
the range between about 400.degree. C. and about 700.degree. C. or
a sub-range thereof, an induction coil arranged to be powered by a
power source supplying alternating current and being positioned so
as to generate an alternating magnetic field within the reactor
unit upon energization by the power source, whereby the
ferromagnetic material is heated to a temperature within said
temperature range T by means of said alternating magnetic
field.
2. A reactor system according to claim 1, wherein the Curie
temperature of the ferromagnetic material equals an operating
temperature at substantially the upper limit of the given
temperature range T of the aromatization reaction.
3. A reactor system according to claim 1, wherein the Curie
temperature of the ferromagnetic material is above about
500.degree. C.
4. A reactor system according to claim 1, wherein the induction
coil is placed within the reactor unit or around the reactor
unit.
5. A reactor system according to claim 1, wherein said
ferromagnetic material comprises one or more ferromagnetic
macroscopic supports susceptible for induction heating, where said
one or more ferromagnetic macroscopic supports are ferromagnetic at
temperatures up to an upper limit of the given temperature range T,
where said one or more ferromagnetic macroscopic supports is/are
coated with an oxide and where the oxide is impregnated with
catalyst material.
6. A reactor system according to claim 1, wherein said catalytic
mixture comprises bodies of catalyst material mixed with bodies of
ferromagnetic material, wherein the smallest outer dimension of a
plurality of the bodies are in the order of about 1-2 mm or
larger.
7. A reactor system according to claim 6, wherein the catalytic
mixture has a predetermined ratio between said bodies of catalyst
material and said bodies of ferromagnetic material.
8. A reactor system according to claim 6, wherein the predetermined
ratio between said catalyst and said ferromagnetic materials is a
predetermined graded ratio varying along a flow direction of said
reactor.
9. A reactor system according to claim 1, wherein the distance
between windings of said induction coil varies along the flow
direction of the reactor.
10. A catalytic mixture arranged for catalyzing aromatization of
higher hydrocarbons in a reactor in a given temperature range T
upon bringing a reactant stream comprising higher hydrocarbons into
contact with said catalytic mixture, said catalytic mixture
comprising a catalyst material and a ferromagnetic material, where
said catalyst material is arranged to catalyze the aromatization of
higher hydrocarbons and said ferromagnetic material is
ferromagnetic at least at temperatures up to an upper limit of the
given temperature range T, wherein the given temperature range T is
the range between about 400.degree. C. and about 700.degree. C. or
a sub-range thereof.
11. A catalytic mixture according to claim 10, wherein said
catalytic mixture comprises bodies of catalyst material mixed with
bodies of ferromagnetic material.
12. A catalytic mixture according to claim 10, wherein the Curie
temperature of the ferromagnetic material substantially equals an
operating temperature at substantially the upper limit of the given
temperature range T of the aromatization reaction.
13. A catalytic mixture according to claim 10, wherein the
ferromagnetic material is a material comprising iron, an alloy
comprising iron and chromium, an alloy comprising iron, chromium
and aluminum, an alloy comprising iron and cobalt, or an alloy
comprising iron, aluminum, nickel and cobalt.
14. A catalytic mixture according to claim 10, wherein the catalyst
material comprises a catalytically active material supported on a
zeolite.
15. A catalytic mixture according to claim 14, wherein said
catalytically active material is an active phase of one or more of
the following elements: zinc, gallium, molybdenum, platinum.
16. A catalytic mixture according to claim 14, wherein said zeolite
is a HZSM, a ZSM or a SAPO zeolite.
17. A catalytic mixture according to claim 10, wherein said
ferromagnetic material comprises one or more ferromagnetic
macroscopic supports susceptible for induction heating, where said
one or more ferromagnetic macroscopic supports are ferromagnetic at
temperatures up to an upper limit of the given temperature range T,
where said one or more ferromagnetic macroscopic supports is/are
coated with an oxide and where the oxide is impregnated with
catalyst material.
18. A catalytic mixture according to claim 10, wherein the
catalytic mixture has a predetermined ratio between said catalyst
material and said ferromagnetic material.
19. A method for aromatization of higher hydrocarbons in a given
temperature range T in a reactor system, said reactor system
comprising a reactor unit arranged to accommodate a catalytic
mixture, said catalytic mixture comprising a catalyst material and
a ferromagnetic material, where said catalyst material is arranged
to catalyze the aromatization of higher hydrocarbons and said
ferromagnetic material is ferromagnetic at least at temperatures up
to an upper limit of the given temperature range T, and an
induction coil arranged to be powered by a power source supplying
alternating current and positioned so as to generate an alternating
magnetic field within the reactor unit upon energization by the
power source, whereby the catalytic mixture is heated to a
temperature within the given temperature range T by means of said
alternating magnetic field, wherein the temperature range T is the
range from between about 400.degree. C. and about 700.degree. C. or
a subrange thereof, said method comprising the steps of: (i)
generating an alternating magnetic field within the reactor unit
upon energization by a power source supplying alternating current,
said alternating magnetic field passing through the reactor unit,
thereby heating catalytic mixture by induction of a magnetic flux
in the material; (ii) bringing a reactant stream comprising higher
hydrocarbons into contact with said catalyst material; (iii)
heating said reactant stream to a temperature within the given
temperature range T within said reactor by the generated
alternating magnetic field; and (iv) letting the reactant stream
react in order to provide a product to be outlet from the
reactor.
20. A method according to claim 19, wherein the reactant stream is
preheated in a heat exchanger prior to step (ii).
Description
[0001] The present invention relates to a reactor system for
aromatization of higher hydrocarbons, to a catalytic mixture
arranged for catalyzing aromatization of higher hydrocarbons in a
reactor, and to a method for aromatization of higher
hydrocarbons.
[0002] Aromatic compounds, such as benzene, toluene and xylene, can
be produced from higher hydrocarbons, such as propane, butane and
pentane. Current state of the art in industrial processes for
aromatization of higher hydrocarbons typically comprises an initial
dehydrogenation of alkanes followed by aromatization of the
alkenes.
[0003] The reaction is thermodynamically controlled and takes place
at temperatures of about 500-700.degree. C., typically without any
co-feed or diluents. Typically, a feed or a reactant stream
comprising higher hydrocarbons is preheated in a separate preheat
section prior to entering the reactor(s) in which the
dehydrogenation and aromatization takes place, and typically the
reaction occurs adiabatically in sequential reactors, possibly with
heating in between.
[0004] The initial dehydrogenation is endothermic, whilst the
subsequent aromatization is exothermic. Overall, the reaction
enthalpy ends up being almost thermo neutral.
[0005] One of the parasitic reactions in dehydrogenation is carbon
formation, which leads to rapid deactivation of the catalyst. Thus,
frequent regenerations of the catalyst may be necessary in certain
applications. Carbon formation is not only a problem for the
catalyst. Also the material used for the dehydrogenation reactor
and for the piping has to be carefully selected, typically by using
highly expensive alloys in order to avoid carbon attack resulting
in the catastrophic form of corrosion known as metal dusting.
[0006] The combination of high temperatures and a dry hydrocarbon
feed in the dehydrogenation and aromatization reaction results in a
high potential for carbon formation in the catalyst bed and the
preheat section.
[0007] It is therefore an object of the present invention to
provide a process, reactor system and catalyst mixture for
aromatization of alkanes which are able to maintain a high
stability of the catalyst and reactor system.
[0008] It is another object of the present invention to provide a
process, reactor system and catalyst mixture for aromatization of
alkanes which are simple and energy efficient and which at the same
time enables maintaining high stability of the catalyst.
[0009] It is also an object of the present invention to provide a
process, reactor system and catalyst mixture wherein the reaction
temperature is controlled accurately. Preferably, the temperature
of the process is lowered compared to hitherto known reactions;
hereby, the thermodynamic potential for dehydrogenation is
increased and parasitic reactions, such as coking and/or cracking
of the catalyst material are reduced.
[0010] The present invention solves one or more of the above
mentioned problems.
[0011] An aspect of the present invention relates to a reactor
system for aromatization of higher hydrocarbons within a given
temperature range T upon bringing a reactant stream comprising
higher hydrocarbons into contact with a catalytic mixture. The
reactor system comprises a reactor unit arranged to accommodate a
catalytic mixture, said catalytic mixture comprising a catalyst
material and a ferromagnetic material, where the catalyst material
is arranged to catalyze the aromatization of higher hydrocarbons
and said ferromagnetic material is ferromagnetic at least at
temperatures up to an upper limit of the given temperature range T,
where the temperature range T is the range from between about
400.degree. C. and about 700.degree. C. or a subrange thereof. The
reactor system also comprises an induction coil arranged to be
powered by a power source supplying alternating current and being
positioned so as to generate an alternating magnetic field within
the reactor unit upon energization by the power source, whereby the
ferromagnetic material is heated to a temperature within said
temperature range T by means of said alternating magnetic
field.
[0012] A key element, which the present invention addresses, is the
issue of supplying heat needed to carry out the dehydrogenation
reaction. The reaction is often carried out in more than one
adiabatic catalytic bed, with reheating in between or in a reactor
with a furnace, e.g. an electric furnace. By the reactor system of
the invention, the heat for the endothermic dehydrogenation
reaction is provided by induction heating. This provides for a
quick heating of the catalyst within the reactor. Moreover, a good
control of the temperature within the reactor system is obtained,
which in turn assists in reducing carbon formation on the catalyst
and in maximizing the conversion of alkanes to alkenes.
[0013] In general, the temperature within the reactor unit may be
kept lower than would be the case with an externally heated reactor
or with a preheated stream. This provides for an improved overall
yield, a better selectivity as well as a quicker start-up of the
process. Moreover, less catalyst degeneration in the form of coking
and cracking will happen, thus reducing the frequency of
regenerations of the catalyst.
[0014] In the reactor system of the invention, the catalytic
mixture, viz. the ferromagnetic material, will be the hottest part
of the system. The temperature difference across the bed will
however be dependent on the actual configuration of the
ferromagnetic material, the catalyst material and the process
conditions.
[0015] Preferably, the coercivity of the ferromagnetic material is
high, so that the amount of heat generated within the ferromagnetic
material and dissipated by the external field in reversing the
magnetization in each magnetization cycle is high.
[0016] As used herein, a material of "high magnetic coercivity",
.sub.BH.sub.C, is seen as a "hard magnetic material" having a
coercivity .sub.BH.sub.C at or above about 20 kA/m, whilst a
material of "low magnetic coercivity" is seen as a "soft magnetic
material" having a coercivity .sub.BH.sub.C at or below about 5
kA/m. It should be understood that the terms "hard" and "soft"
magnetic materials are meant to refer to the magnetic properties of
the materials, not their mechanical properties.
[0017] As used herein, the term "temperature range T" is meant to
denote a desired range of temperatures, typically up to an upper
limit thereof, at which the dehydrogenation reaction is to take
place within the reactor system during operation. The temperature
range T is the range from between about 400.degree. C. and about
700.degree. C. or a subrange thereof. Preferred subranges are e.g.
the range from between about 450.degree. C. and about 700.degree.
C., the range from between about 500.degree. C. and about
700.degree. C., the range from between about 550.degree. C. and
about 700.degree. C., or the range from between about 550.degree.
C. and about 650.degree. C.
[0018] As used herein, the term "higher hydrocarbons" is meant to
denote organic compound consisting entirely of hydrogen and carbon
and including at least three carbon molecules.
[0019] Ferromagnetic material provides for further advantages, such
as: [0020] A ferromagnetic material absorbs a high proportion of
the magnetic field, thereby making the need for shielding less or
even superfluous. [0021] Heating of ferromagnetic materials is
relatively faster and cheaper than heating of non-ferromagnetic
materials. A ferromagnetic material has an inherent or intrinsic
maximum temperature of heating, viz. the Curie temperature.
Therefore, the use of a catalyst material which is ferromagnetic
ensures that an endothermic chemical reaction is not heated above a
specific temperature, viz. the Curie temperature. Thus, it is
ensured that the chemical reaction will not run out of control.
[0022] Another advantage of the invention is that the temperature
of the reactor unit can be kept lower than the temperature of the
conventionally used adiabatic reactor. The lower temperature is
beneficial for the overall yield of the process and required
regenerations for carbon removal will be less frequent since
parasitic reactions like coking and cracking are reduced. Further
advantages comprise the possibility of tuning the exit temperature,
which increases the thermodynamic potential for
dehydrogenation.
[0023] The induction coil may e.g. be placed within the reactor
unit or around the reactor unit. If the induction coil is placed
within the reactor unit, it is preferable that it is positioned at
least substantially adjacent to the inner wall(s) of the reactor
unit in order to surround as much of the catalytic mixture as
possible. In the cases, where the induction coil is placed within
the reactor unit, windings of the reactor unit may be in physical
contact with catalyst material. In this case, in addition to the
induction heating, the catalyst material may be heated directly by
ohmic/resistive heating due to the passage of electric current
through the windings of the induction coil. The reactor unit is
typically made of non-ferromagnetic material.
[0024] In conclusion, the invention provides a reactor system
arranged to carry out aromatization of higher hydrocarbons cheaper
and with better selectivity than current reactor systems. Moreover,
the lifetime of the catalyst will be improved due to the lower
average operation temperature within the reactor system.
[0025] In an embodiment, the Curie temperature of the ferromagnetic
material equals an operating temperature at substantially the upper
limit of the given temperature range T of the aromatization
reaction. The term "aromatization reaction" is meant to denote the
full reaction from dehydrogenation of alkanes to alkenes and the
subsequent aromatization of alkenes to aromatic compound, unless it
is specified that the term only denotes the subsequent
aromatization of alkenes to aromatic compounds.
[0026] The Curie temperature of the ferromagnetic material could be
close to, above or far above the upper limit of the given
temperature range T. In an embodiment the Curie temperature equals
an operating temperature at substantially the upper limit of the
given temperature range T, thereby providing an upper limit of the
temperature range T
[0027] Hereby, it is ensured that the dehydrogenation reaction is
not heated above a specific temperature, viz. the Curie
temperature. Thus, it is ensured that the temperature does not
become too high; it is well known that excessive temperatures may
give rise to significant coke formation due to thermal cracking.
Thus, designing the composition of the catalyst in order to design
the Curie temperature renders it possible to provide a catalyst
that will be less prone to carbon formation.
[0028] In an embodiment, the Curie temperature of the ferromagnetic
material is above about 500.degree. C. Typically the Curie
temperature of the ferromagnetic material is below about
1000.degree. C. As an example only, the ferromagnetic material is
FeCrAlloy with a Curie temperature of about 560.degree. C.
[0029] In an embodiment, the induction coil is placed within the
reactor unit or around the reactor unit. The coil may e.g. be made
of copper, constantan, an iron-chromium-aluminium (FeCrAl) alloy,
an alloy of copper, manganese, and nickel, and combinations
thereof. An iron-chromium-aluminum alloy is e.g. sold under the
trademark "Kanthal", and an alloy of copper, manganese and nickel
is sold under the trademark "Manganin". The examples of the
material of the induction coil are advantageous due to their low
resistivity and high temperature stability. Other materials which
fulfil these requirements could also be considered for the
application.
[0030] In an embodiment, the ferromagnetic material comprises one
or more ferromagnetic macroscopic supports susceptible for
induction heating, where the one or more ferromagnetic macroscopic
supports are ferromagnetic at temperatures up to an upper limit of
the given temperature range T, where the one or more ferromagnetic
macroscopic supports is/are coated with an oxide and where the
oxide is impregnated with catalyst material. The ferromagnetic
material may e.g. be cobalt, iron, nickel, an alnico alloy, a FeCr
alloy, Permendur or combinations thereof.
[0031] The oxide may also be impregnated with ferromagnetic
particles. Thus, when the catalyst material is subjected to a
varying magnetic field, both the ferromagnetic macroscopic support
and the ferromagnetic particles impregnated into the oxide of the
ferromagnetic macroscopic support are heated. Whilst the
ferromagnetic macroscopic support heats the catalyst material from
within, the ferromagnetic particles heats from the outside of the
oxide. Thereby, a higher temperature and/or a higher heating rate
are/is achievable.
[0032] As used herein, the term "macroscopic support" is meant to
denote a macroscopic support material in any appropriate form
providing a high surface. Non-limiting examples are metallic
elements, monoliths or miniliths. The macroscopic support may have
a number of channels; in this case it may be straight-channeled or
a cross-corrugated element. The material of the macroscopic support
may be porous or the macroscopic support may be a solid. The word
"macroscopic" in "macroscopic support" is meant to specify that the
support is large enough to be visible with the naked eye, without
magnifying devices.
[0033] In an embodiment, the catalytic mixture comprises bodies of
catalyst material mixed with bodies of ferromagnetic material,
wherein the smallest outer dimension of a plurality of the bodies
are in the order of about 1-2 mm or larger. Preferably, the
smallest outside dimension of the bodies are between about 2-3 mm
to about 8 mm. The bodies of catalyst material are e.g. extrudates
or miniliths. The bodies of ferromagnetic material may e.g. be iron
spheres. The term "miniliths" is meant to denote a small monolith;
a reactor may typically house a large number of miniliths. The
catalytic mixture preferably has a predetermined ratio between said
bodies of catalyst material and said bodies of ferromagnetic
material. The predetermined ratio between said catalyst and said
ferromagnetic materials is preferably a predetermined graded ratio
varying along a flow direction of said reactor. Hereby, it is
possible to control the temperature in different zones of the
reactor. A radial flow reactor may be used; in this case, the
predetermined ration varies along the radial direction of the
reactor. Alternatively, an axial flow reactor may be used. The
ferromagnetic material may e.g. be cobalt, iron, nickel, an alnico
alloy, a FeCr alloy, Permendur or combinations thereof.
[0034] In an embodiment, the distance between windings of said
induction coil varies along the flow direction of the reactor.
Hereby, the heating within the reactor may be graded by varying the
distance between windings of the induction coil. Thus, the distance
between successive windings should be larger towards the inlet end
of the reactor than towards the outlet end, in order to obtain a
higher rate of heating towards the inlet end compared to the
heating rate towards the outlet end of the reactor.
[0035] Alternative or additionally, the catalyst material may
comprise two or more types of catalytic mixtures along the catalyst
bed, where the two or more types of catalytic mixtures have
different Curie temperatures. If the catalytic mixture closest to
the inlet of the reactor unit has a lower Curie temperature than
the catalytic mixture closest to the outlet of the reactor, it is
possible to control the maximum temperature achievable within the
reactor so that it is less close to the inlet end than further
along the reactor unit.
[0036] Another aspect of the invention relates to a catalytic
mixture arranged for catalyzing aromatization of higher
hydrocarbons in a reactor in a given temperature range T upon
bringing a reactant stream comprising higher hydrocarbons into
contact with said catalytic mixture, where the temperature range T
is the range from between about 400.degree. C. and about
700.degree. C. or a subrange thereof. The catalytic mixture
comprises a catalyst material and a ferromagnetic material, where
the catalyst material is arranged to catalyze the aromatization of
higher hydrocarbons and the ferromagnetic material is ferromagnetic
at least at temperatures up to an upper limit of the given
temperature range T.
[0037] In an embodiment, the catalytic mixture comprises bodies of
catalyst material mixed with bodies of ferromagnetic material.
[0038] In an embodiment, the Curie temperature of the ferromagnetic
material substantially equals an operating temperature at
substantially the upper limit of the given temperature range T of
the aromatization reaction.
[0039] In an embodiment, the ferromagnetic material is a material
comprising iron, an alloy comprising iron and chromium, an alloy
comprising iron, chromium and aluminum, an alloy comprising iron
and cobalt, or an alloy comprising iron, aluminum, nickel and
cobalt.
[0040] In an embodiment, the catalyst material comprises a
catalytically active material supported on a zeolite. The
catalytically active material is e.g. an active phase of one or
more of the following elements: zinc, gallium, molybdenum,
platinum; and the zeolite is e.g. a HZSM, a ZSM or a SAPO zeolite.
Thus, an example of the catalyst mixture is a catalytically active
material, e.g. Zn, supported on e.g. HZSM-5.
[0041] In an embodiment, the ferromagnetic material of the
catalytic mixture comprises one or more ferromagnetic macroscopic
supports susceptible for induction heating, where said one or more
ferromagnetic macroscopic supports are ferromagnetic at
temperatures up to an upper limit of the given temperature range T,
where said one or more ferromagnetic macroscopic supports is/are
coated with an oxide and where the oxide is impregnated with
catalyst material. Non-limiting examples of ferromagnetic
macroscopic supports coated with an oxide, which in turn is
impregnated with catalyst material, are metallic elements,
monoliths or miniliths. The ferromagnetic material may e.g. be
cobalt, iron, nickel, an alnico alloy, a FeCr alloy, Permendur or
combinations thereof
[0042] In an embodiment, the catalytic mixture has a predetermined
ratio between said catalyst material and said ferromagnetic
material.
[0043] In an embodiment, the catalytic mixture has a predetermined
ratio between the catalyst and the ferromagnetic materials. The
predetermined ratio between the catalyst and the ferromagnetic
materials may be a predetermined graded ratio varying along a flow
direction of the reactor. Hereby, when the catalytic mixture is
used in a reactor, it is possible to control the temperature in
different zones of the reactor. A radial flow reactor may be used;
in this case, the predetermined ratio varies along the radial
direction of the reactor.
[0044] In an embodiment, catalyst material powder and ferromagnetic
material powder are mixed and treated to provide bodies of
catalytic mixture, the bodies having a predetermined ratio between
catalyst and ferromagnetic materials. In an embodiment, the
catalytic mixture comprises bodies of catalyst material mixed with
bodies of ferromagnetic material. Such bodies may e.g. be pellets,
extrudates or miniliths.
[0045] Another aspect of the invention relates to a method for
aromatization of higher hydrocarbons in a given temperature range T
in a reactor system, where the reactor system comprises a reactor
unit arranged to accommodate a catalytic mixture, and where the
catalytic mixture comprises a catalyst material and a ferromagnetic
material. The catalyst material is arranged to catalyze the
aromatization of higher hydrocarbons and the ferromagnetic material
is ferromagnetic at least at temperatures up to an upper limit of
the given temperature range T, where the temperature range T is the
range from between about 400.degree. C. and about 700.degree. C. or
a subrange thereof. The reactor system further comprises an
induction coil arranged to be powered by a power source supplying
alternating current and positioned so as to generate an alternating
magnetic field within the reactor unit upon energization by the
power source, whereby the catalytic mixture is heated to a
temperature within the given temperature range T by means of said
alternating magnetic field. The method comprises the steps of:
[0046] (i) Generating an alternating magnetic field within the
reactor unit upon energization by a power source supplying
alternating current, said alternating magnetic field passing
through the reactor unit, thereby heating catalytic mixture by
induction of a magnetic flux in the material; [0047] (ii) bringing
a reactant stream comprising higher hydrocarbons into contact with
said catalyst material; [0048] (iii) heating said reactant stream
to a temperature within the given temperature range T within said
reactor by the generated alternating magnetic field; and [0049]
(iv) letting the reactant stream react in order to provide a
product to be outlet from the reactor.
[0050] The sequence of the steps (i) to (iv) is not meant to be
limiting. Steps (ii) and (iii) may happen simultaneously, or step
(iii) may be initiated before step (ii) and/or take place at the
same time as step (iv). Advantages as explained in relation to the
reactor system and the catalytic mixture also apply to the method
for aromatization of higher hydrocarbons. The catalytic mixture may
have a predetermined ratio between the catalyst material and the
ferromagnetic material.
[0051] The Curie temperature of the ferromagnetic material may be
equal to or above an upper limit of the given temperature range T
of the dehydrogenation reaction. Alternatively, the Curie
temperature could be slightly lower than the upper limit of the
given temperature range T, in that the reactant gas stream entering
the reactor system may be heated to a temperature above the Curie
temperature before entering the reactor system, thereby providing
an upper limit of the temperature range T--in an upstream part of
the reactor unit--which is higher than that obtainable by induction
heating.
[0052] In an embodiment, the reactant stream is preheated in a heat
exchanger prior to step (ii). This improves the overall energy
efficiency of the process. As an example only, the reactant stream
may be heated to a temperature of between 75.degree. C. and
150.degree. C.
BRIEF DESCRIPTION OF THE FIGURES
[0053] FIG. 1 is a graph showing a temperature profile of catalyst
in a reactor unit heated by induction heating as compared to a
preheated reactant stream;
[0054] FIGS. 2A and 2B show schematic drawings of two embodiments
of a reactor system.
DETAILED DESCRIPTION OF THE FIGURES
[0055] FIG. 1 is a graph showing a temperature profile of catalyst
in a reactor unit heated by induction heating as compared to a
preheated reactant stream.
[0056] In both situations, the reactor unit is a longitudinal flow
reactor unit comprising catalyst material arranged for carrying out
aromatization of higher hydrocarbons, viz. an endothermic reaction.
As shown in FIG. 1 this reaction takes place at temperatures
between about 550.degree. C. and 700.degree. C.
[0057] The dotted line indicates the temperature profile along the
length of a reactor for a preheated reactant stream, corresponding
to the situation where the reactor is an adiabatic reactor. As
shown in FIG. 1, the reactant gas in the situation where the
reactor unit is an adiabatic reactor is preheated to a temperature
of about 700.degree. C. When the gas passes along the longitudinal
direction of the reactor unit, the temperature thereof decreases
since the value of the Gibbs free energy of the aromatization
reaction is negative. In order to ensure that the temperature of
the reactant stream stays above about 550.degree. C. throughout the
reactor length, the reactant gas stream has been preheated to about
700.degree. C. even though such a relatively high temperature
results in a high risk of carbon formation in the catalyst bed of
the reactor.
[0058] In comparison, the solid curve shows the temperature
throughout the longitudinal direction of the reactor unit in a case
where the reactor system and catalyst within the reactor system is
arranged for inductive heating. In the situation shown in FIG. 1,
the reactant gas stream enters the reactor unit at a temperature of
about 150.degree. C. Within the first approximately 10% of the
length of the reactor unit, the temperature of the reactant gas
stream increases to about 550.degree. C. due to the inductive
heating of the catalyst within the reactor unit. The temperature of
the gas within the reactor remains at about 550.degree. C.
throughout the remaining 90% of the length of the reactor unit.
[0059] In addition to the advantageous delivery of heat directly to
the catalyst material and the resulting possibility of reducing the
maximum temperature of the feed or reactant gas, induction heating
offers a fast heating mechanism, which potentially could make
upstart of a aromatization reactor relative fast.
[0060] FIGS. 2A and 2B show schematic drawings of two embodiments
100a and 100b, of a reactor system. In FIGS. 2A and 2B, similar
features are denoted using similar reference numbers.
[0061] FIG. 2A shows an embodiment of the reactor system 100a for
carrying out dehydrogenation of alkanes to alkenes and subsequent
aromatization of the alkenes upon bringing a reactant stream
comprising alkanes into contact with a catalytic mixture 120. The
reactor system 100a comprises a reactor unit 110 arranged to
accommodate a catalytic mixture 120 comprising a catalyst material
and a ferromagnetic material, where the catalyst material is
arranged to catalyze the dehydrogenation of alkanes to alkenes and
the subsequent aromatization of alkenes. The ferromagnetic material
is ferromagnetic at least at temperatures up to about 600.degree.
C.
[0062] Reactant is introduced into the reactor unit 110 via an
inlet 111, and reaction products formed on the surface of the
catalyst mixture 120 is outlet via an outlet 112.
[0063] The reactor system 100a further comprises an induction coil
150a arranged to be powered by a power source 140 supplying
alternating current. The induction coil 150a is connected to the
power source 140 by conductors 152. The induction coil 150a is
positioned so as to generate an alternating magnetic field within
the reactor unit 110 upon energization by the power source 140.
Hereby the catalyst mixture 120 is heated to a temperature within a
given temperature range T relevant for dehydrogenation of alkanes,
such as between 350.degree. C. and about 500.degree. or 700.degree.
C., by means of the alternating magnetic field.
[0064] The induction coil 150a of FIG. 2A is placed substantially
adjacent to the inner surface of the reactor unit 110 and in
physical contact with the catalytic mixture 120. In this case, in
addition to the induction heating provided by the magnetic field,
the catalyst material 120 adjacent the induction coil 150a is
additionally heated directly by ohmic/resistive heating due to the
passage of electric current through the windings of the induction
coil 150a. The induction coil 150a may be placed either inside or
outside the catalyst basket (not shown) supporting the catalytic
mixture 120 within the reactor unit 110. The induction coil is
preferably made of kanthal.
[0065] The catalytic mixture 120 may be divided into sections (not
shown in the figures), where the ratio between the catalytic
material and the ferromagnetic material is varies from one section
to another. At the inlet of the reactor unit 110, the reaction rate
is high and the heat demand is large; this may be compensated for
by having a relatively large proportion of ferromagnetic material
compared to the catalytic material. The ferromagnetic material may
also be designed to limit the temperature by choosing a
ferromagnetic material with a Curie temperature close to the
desired reaction temperature.
[0066] Placing the induction coil 150a within the reactor unit 110
ensures that the heat produced due to ohmic resistance heating of
the induction coil 150a remains useful for the dehydrogenation
reaction. However, having an oscillating magnetic field within the
reactor may cause problems, if the materials of the reactor unit
110 are magnetic with a high coercivity, in that undesirably high
temperatures may be the result. This problem can be circumvented by
cladding the inside of the reactor unit 110 with materials capable
of reflecting the oscillating magnetic field. Such materials could
e.g. be good electrical conductors, such as copper. Alternatively,
the material of the reactor unit 110 could be chosen as a material
with a very low coercivity. Alternatively, the induction coil 150
could be wound as a torus.
[0067] To make the catalyst bed susceptible for induction,
different approaches may be applied. One approach is to support the
catalyst material on the ferromagnetic material. For example, the
ferromagnetic material comprises one or more ferromagnetic
macroscopic supports susceptible for induction heating, and the one
or more ferromagnetic macroscopic supports are ferromagnetic at
temperatures up to an upper limit of the given temperature range T.
The one or more ferromagnetic macroscopic supports is/are coated
with an oxide and the oxide is impregnated with catalyst material.
Another approach is to mix catalyst material powder and
ferromagnetic material powder and treat the mixture to provide
bodies of catalytic mixture. Additionally or alternatively, the
catalytic mixture comprises bodies of catalyst material mixed with
bodies of ferromagnetic material, wherein the smallest outside
dimension of the bodies are in the order of about 1-2 mm or
larger.
[0068] The catalytic mixture preferably has a predetermined ratio
between the catalyst material and the ferromagnetic material. This
predetermined ratio may be a graded ratio varying along a flow
direction of the reactor.
[0069] In another approach, ferromagnetic macroscopic supports are
coated with an oxide impregnated with the catalytically active
material. This approach offers a large versatility compared to the
ferromagnetic nanoparticles in the catalyst, as the choice of
catalytic active phase is not required to be ferromagnetic.
[0070] FIG. 2B shows another embodiment 100b of the reactor system
for carrying out dehydrogenation of alkanes to alkenes and
subsequent aromatization of the alkenes upon bringing a reactant
stream comprising alkanes into contact with a catalytic mixture
120. The reactor unit 110 and its inlet and outlet 111, 112, the
catalytic mixture 120, the power source 140 and its connecting
conductors 152 are similar to those of the embodiment shown in FIG.
2A.
[0071] In the embodiment of FIG. 2B, an induction coil 150b is
wound or positioned around the outside of the reactor unit 110.
[0072] In both embodiments shown in FIGS. 2A and 2B, the catalytic
mixture can be any catalytic mixture according to the invention.
Thus, the catalytic mixture may be in the form of catalyst material
supported on the ferromagnetic material, e.g. where in the form of
ferromagnetic macroscopic support(s) coated with an oxide, where
the oxide is impregnated with catalyst material, miniliths, a
monolith, or bodies produced from a mixture of catalyst material
powder and ferromagnetic material powder. Thus, the catalyst
material is not limited to catalyst material having relative size
as compared to the reactor system as shown in the figures.
Moreover, when the catalyst material comprises a plurality of
macroscopic supports, the catalyst material would typically be
packed so as to leave less space between the macroscopic supports
than shown in the FIGS. 2A and 2B. Furthermore, in the two
embodiments shown in FIGS. 2A and 2B, the reactor unit 110 is made
of non-ferromagnetic material. In the two embodiments shown in
FIGS. 2A and 2B, the power source 140 is an electronic oscillator
arranged to pass a high-frequency alternating current (AC) through
the coil surrounding at least part of the catalyst material within
the reactor system.
Example
[0073] The catalyst material comprises for example Zn as the
catalytically active material supported on a zeolite, e.g. a HZSM,
a ZSM or a SAPO zeolite. The ferromagnetic material is e.g. beads
of iron, an alloy comprising iron and chromium, an alloy comprising
iron, chromium and aluminum, an alloy comprising iron and cobalt,
or an alloy comprising iron, aluminum, nickel and cobalt.
[0074] The frequency of the alternating current through the
induction coil is e.g. 50 kHz and the alternating current has e.g.
a root mean square value of 10 A. Such an alternating current field
generates a magnetic field of about 0.05 T. The magnetic field
heats the ferromagnetic material, e.g. the FeCrAlloy beads, to a
temperature of about 550.degree. C. and the energy is transferred
to the catalyst material. When a reactant stream entering the
reactor at a temperature of about 100.degree. C., it is rapidly
heated to 550.degree. C. which will facilitate aromate synthesis
over the catalyst material. The product from the reaction is a
mixture of benzene, toluene, xylene, hydrocarbons and hydrogen. In
a further step, the product from the reaction may be purified.
[0075] Although the present invention has been described in
connection with the specified embodiments, it should not be
construed as being in any way limited to the presented examples.
The scope of the present invention is set out by the accompanying
claim set. In the context of the claims, the terms "comprising" or
"comprises" do not exclude other possible elements or steps. Also,
the mentioning of references such as "a" or "an" etc. should not be
construed as excluding a plurality. Furthermore, individual
features mentioned in different claims may possibly be
advantageously combined, and the mentioning of these features in
different claims does not exclude that a combination of features is
not possible and advantageous.
* * * * *